diff --git a/esphome/components/api/api_buffer.h b/esphome/components/api/api_buffer.h
index 00801e3ee5..1d0cccf61c 100644
--- a/esphome/components/api/api_buffer.h
+++ b/esphome/components/api/api_buffer.h
@@ -44,6 +44,12 @@ class APIBuffer {
     this->reserve(n);
     this->size_ = n;  // no zero-fill
   }
+  /// Reserve capacity for max(reserve_size, new_size) bytes, then set size to new_size.
+  /// Single grow_ check regardless of argument order.
+  inline void reserve_and_resize(size_t reserve_size, size_t new_size) ESPHOME_ALWAYS_INLINE {
+    this->reserve(std::max(reserve_size, new_size));
+    this->size_ = new_size;
+  }
   uint8_t *data() { return this->data_.get(); }
   const uint8_t *data() const { return this->data_.get(); }
   size_t size() const { return this->size_; }
diff --git a/esphome/components/api/api_connection.cpp b/esphome/components/api/api_connection.cpp
index dea3ba5460..d55b5dffb6 100644
--- a/esphome/components/api/api_connection.cpp
+++ b/esphome/components/api/api_connection.cpp
@@ -2025,8 +2025,7 @@ uint16_t APIConnection::encode_to_buffer(uint32_t calculated_size, MessageEncode
     // Batch message second or later
     // Add padding for previous message footer + this message header
     size_t current_size = shared_buf.size();
-    shared_buf.reserve(current_size + total_calculated_size);
-    shared_buf.resize(current_size + footer_size + header_padding);
+    shared_buf.reserve_and_resize(current_size + total_calculated_size, current_size + footer_size + header_padding);
   }
 
   // Pre-resize buffer to include payload, then encode through raw pointer
diff --git a/esphome/components/api/api_connection.h b/esphome/components/api/api_connection.h
index 68f698d190..85c8e777a9 100644
--- a/esphome/components/api/api_connection.h
+++ b/esphome/components/api/api_connection.h
@@ -305,9 +305,9 @@ class APIConnection final : public APIServerConnectionBase {
     // Reserve space for header padding + message + footer
     // - Header padding: space for protocol headers (7 bytes for Noise, 6 for Plaintext)
     // - Footer: space for MAC (16 bytes for Noise, 0 for Plaintext)
-    shared_buf.reserve(total_size);
-    // Resize to add header padding so message encoding starts at the correct position
-    shared_buf.resize(header_padding);
+    // Reserve full size but only set initial size to header padding
+    // so message encoding starts at the correct position
+    shared_buf.reserve_and_resize(total_size, header_padding);
   }
 
   // Convenience overload - computes frame overhead internally
diff --git a/esphome/components/api/api_frame_helper.h b/esphome/components/api/api_frame_helper.h
index 5e07ad43a9..b2561f2b32 100644
--- a/esphome/components/api/api_frame_helper.h
+++ b/esphome/components/api/api_frame_helper.h
@@ -147,22 +147,18 @@ class APIFrameHelper {
   //
   void set_nodelay_for_message(bool is_log_message) {
     if (!is_log_message) {
-      if (this->nodelay_state_ != NODELAY_ON) {
+      if (this->nodelay_counter_) {
         this->set_nodelay_raw_(true);
-        this->nodelay_state_ = NODELAY_ON;
+        this->nodelay_counter_ = 0;
       }
       return;
     }
-
-    // Log messages: state transitions -1 -> 1 -> ... -> LOG_NAGLE_COUNT -> -1 (flush)
-    if (this->nodelay_state_ == NODELAY_ON) {
+    // Log message: enable Nagle on first, flush after LOG_NAGLE_COUNT
+    if (!this->nodelay_counter_)
       this->set_nodelay_raw_(false);
-      this->nodelay_state_ = 1;
-    } else if (this->nodelay_state_ >= LOG_NAGLE_COUNT) {
+    if (++this->nodelay_counter_ > LOG_NAGLE_COUNT) {
       this->set_nodelay_raw_(true);
-      this->nodelay_state_ = NODELAY_ON;
-    } else {
-      this->nodelay_state_++;
+      this->nodelay_counter_ = 0;
     }
   }
   virtual APIError write_protobuf_packet(uint8_t type, ProtoWriteBuffer buffer) = 0;
@@ -258,18 +254,17 @@ class APIFrameHelper {
   uint8_t tx_buf_head_{0};
   uint8_t tx_buf_tail_{0};
   uint8_t tx_buf_count_{0};
-  // Nagle batching state for log messages. NODELAY_ON (-1) means NODELAY is enabled
-  // (immediate send). Values 1..LOG_NAGLE_COUNT count log messages in the current Nagle batch.
-  // After LOG_NAGLE_COUNT logs, we switch to NODELAY to flush and reset.
+  // Nagle batching counter for log messages. 0 means NODELAY is enabled (immediate send).
+  // Values 1..LOG_NAGLE_COUNT count log messages in the current Nagle batch.
+  // After LOG_NAGLE_COUNT logs, we flush by re-enabling NODELAY and resetting to 0.
   // ESP8266 has the tightest TCP send buffer (2×MSS) and needs conservative batching.
   // ESP32 (4×MSS+), RP2040 (8×MSS), and LibreTiny (4×MSS) can coalesce more.
-  static constexpr int8_t NODELAY_ON = -1;
 #ifdef USE_ESP8266
-  static constexpr int8_t LOG_NAGLE_COUNT = 2;
+  static constexpr uint8_t LOG_NAGLE_COUNT = 2;
 #else
-  static constexpr int8_t LOG_NAGLE_COUNT = 3;
+  static constexpr uint8_t LOG_NAGLE_COUNT = 3;
 #endif
-  int8_t nodelay_state_{NODELAY_ON};
+  uint8_t nodelay_counter_{0};
 
   // Internal helper to set TCP_NODELAY socket option
   void set_nodelay_raw_(bool enable) {